Melt processable thermotropic wholly aromatic polyester comprising both para-oxybenzoyl and meta-oxybenzoyl moieties

ABSTRACT

A wholly aromatic polyester is provided which unlike the aromatic polyesters normally encountered in the prior art is not intractable or difficultly tractable and readily undergoes melt processing with ease. The aromatic polyester of the present invention consists essentially of the recurring units (a) p-oxybenzoyl moiety, (b) m-oxybenzoyl moiety, (c) 2,6-dicarboxynaphthalene moiety, and (d) symmetrical dioxy aryl moiety (as defined), and is free of units which possess ring substitution. The resulting polyester exhibits a melting point below approximately 310° C., and preferably below 300° C. The ability of the wholly aromatic polyester readily to undergo melt processing can be attributed to its atypical inherent propensity to form a thermotropic melt phase at relatively low temperatures. The wholly aromatic polyester may be formed by a variety of procedures including a slurry polymerization technique (as defined) or a melt polymerization technique. The presence of the meta-oxybenzoyl moiety in the wholly aromatic polyester (as described) has been found to render the polymer melt processable at even lower temperatures than if this component were omitted.

BACKGROUND OF THE INVENTION

Wholly aromatic polyester resins have long been known. For instance,p-hydroxybenzoic acid homopolymer and copolymers have been provided inthe past and are commercially available. Those wholly aromaticpolyesters normally encountered in the prior art have tended to besomewhat intractable in nature and to present substantial difficultiesif one attempts to melt process the same while employing conventionalmelt processing procedures. Such polymers commonly are crystalline innature, relatively high melting or possess a decomposition temperaturewhich is below the melting point, and when molten frequently exhibit anisotropic melt phase. Molding techniques such as compression molding orsintering may be utilized with such material; however, injectionmolding, melt spinning, etc. commonly have not been viable alternativesor when attempted commonly have been accomplished with difficulty. Suchpolymers commonly cannot be melt extruded to form nondegraded fibers.Even those wholly aromatic polymers which exhibit a melting point belowtheir decomposition temperature commonly melt at such high temperaturesthat quality fibers may not be melt spun. For instance, fibers meltextruded at extremely high temperatures commonly possess a voidyinternal structure and diminished tensile properties.

Representative publications which discuss wholly aromatic polyestersinclude: (a) Polyesters of Hydroxybenzoic Acids, by Russell Gilkey andJohn R. Caldwell, J. of Applied Polymer Sci., Vol. II, Pages 198 to 202(1959), (b) Polyarylates (Polyesters From Aromatic Dicarboxylic Acidsand Bisphenols), by G. Bier, Polymer, Vol. 15, Pages 527 to 535 (August1974), (c) Aromatic Polyester Plastics, by S.G. Cottis, Modern Plastics,Pages 62 to 63 (July 1975), and (d) Poly (p-Oxybenzoyl Systems):Homopolymer for Coatings: Copolymers for Compression and InjectionMolding, by Roger S. Storm and Steve G. Cottis, Coatings Plast.Preprint, Vol. 34, No. 1, Pages 194 to 197 (April 1974). See also, U.S.Pat. Nos. 3,039,994; 3,169,121; 3,321,437; 3,553,167; 3,637,595;3,651,014; 3,723,388; 3,759,870; 3,767,621; 3,787,370; 3,790,528;3,829,406; 3,890,256; and 3,975,487.

Also, it more recently has been disclosed that certain polyesters may beformed which exhibit melt anisotropy. See for instance, (a) PolyesterX7G-A Self Reinforced Thermoplastic, by W.J. Jackson Jr., H. F. Kuhfuss,and T. F. Gray, Jr., 30th Anniversary Technical Conference, 1975Reinforced Plastics/Composites Institute, The Society of the PlasticsIndustry, Inc., Section 17-D, Pages 1 to 4, (b) Belgian Pat. Nos.828,935 and 828,936, (c) Dutch No. 7505551, (d) West German Nos. 2520819and 2520820, (e) Japanese No. 43-223, (f) U.S. Pat. Nos. 3,991,013 and3,991,014.

It is an object of the present invention to provide an improved meltprocessable wholly aromatic polyester.

It is an object of the present invention to provide an improved meltprocessable wholly aromatic polyester which is free of ring substitutionand which is suited for the formation of molded articles and meltextruded fibers.

It is an object of the present invention to provide an improved meltprocessable aromatic polyester capable of forming a thermotropic meltphase at a temperature below approximately 310° C., preferably belowapproximately 300° C.

It is an object of the present invention to provide an improved whollyaromatic polyester which exhibits a melting point well below itsdecomposition temperature.

It is an object of the present invention to provide an improved whollyaromatic polyester which is crystalline in nature and highly tractable.

It is an object of the present invention to provide an improved whollyaromatic polyester which readily may be injection molded to form amolded article.

It is an object of the present invention to provide an improved whollyaromatic polyester which exhibits a melting point well below itsdecomposition temperature and which may form fibers with ease.

These and other objects, as well as the scope, nature and utilization ofthe invention will be apparent from the following detailed description.

In commonly assigned U.S. Ser. No. 686,189, filed May 13, 1976 (now U.S.Pat. No. 4,067,852), by Gordon W. Calundann entitled "Improved MeltProcessable Thermotropic Wholly Aromatic Polyester and Process for ItsProduction" is claimed a generic invention wherein a wholly aromaticpolyester (as defined) consists essentially of recurring units ofp-oxybenzoyl moiety, 2,6-dicarboxynaphthalene moiety, and symmetricaldioxy aryl moiety.

In commonly assigned U.S. Ser. No. 789,374, filed Apr. 20, 1977 (nowU.S. Pat. No. 4,083,829) by Gordon W. Calundann, Herbert L. Davis,Frederick J. Gorman, and Robert M. Mininni, entitled "Improved MeltProcessable Thermotropic Wholly Aromatic Polyester Which Is ParticularlySuited For Fiber Formation" is specifically claimed a species of thegeneric invention defined in U.S. Ser. No. 686,189 wherein anisophthaloyl moiety and/or meta-dioxy phenyl moiety recur in the whollyaromatic polyester in addition to p-oxybenzoyl moiety,2,6-dicarboxynaphthalene moiety, and symmetrical dioxy aryl moiety.

In commonly assigned U.S. Ser. No. 832,147 filed concurrently herewithby Gordon W. Calundann, entitled "Melt Processable Thermotropic WhollyAromatic Polyester" and now abandoned, is claimed a wholly aromaticpolyester (as defined) which consists essentially of recurring units ofp-oxybenzoyl moiety, 2,6-dioxynaphthalene moiety, and terephthaloylmoiety.

SUMMARY OF THE INVENTION

It has been found that a melt processable wholly aromatic polyestercapable of forming a thermotropic melt phase at a temperature belowapproximately 310° C. consists essentially of the recurring moieties I,II, III, and IV wherein: ##STR1##

IV is a symmetrical dioxy aryl moiety of the formula --O--Ar--O -- whereAr is a divalent radical comprising at least one aromatic ring, whereinthe polyester comprises approximately 30 to 70 mole percent of moiety Iand approximately 3 to 10 mole percent of moiety II. In a preferredembodiment the thermotropic melt phase is formed at a temperature belowapproximately 290° C., and in a particularly preferred embodiment moietyIV is: ##STR2##

DESCRIPTION OF PREFERRED EMBODIMENTS

The wholly aromatic polyester of the present invention consistsessentially of four recurring moieties which when combined in thepolyester have been found to form an atypical thermotropic melt phase ata temperature below approximately 310° C., and preferably belowapproximately 300° C. It has been found that the melting temperatureinitially exhibited by the wholly aromatic polymer when it is melted forthe first time following its formation may be slightly elevated abovethe relatively stable or constant temperature at which it melts uponsubsequent heatings of the solid polymer. Any reference to meltingtemperatures referred to herein accordingly is with reference to suchsubsequent stable melting temperatures exhibited by the unannealedpolyester unless otherwise specified. Such stable melting temperaturesmay be confirmed by the use of a differential scanning calorimeteremploying repeat scans at a 20° C. per minute heat-up rate. Each moietyof the wholly aromatic polyester is free of ring substitution other thanthe linking bonds which form the main polymer chain. Such aromaticpolyester is crystalline in nature and because of its ability to exhibitordered anisotropic properties (i.e., liquid crystals) in the meltreadily can be melt processed with ease. The usual difficulties incurredwhen one attempts to melt process aromatic polyesters by conventionalmelt processing techniques effectively are eliminated. The aromaticpolyester is considered to be "wholly" aromatic in the sense that eachmoiety present in the same contributes at least one aromatic ring to thepolymer backbone.

The wholly aromatic polyester consists essentially of four essentialmoieties. Moiety I can be termed a p-oxybenzoyl moiety and possess thestructural formula: ##STR3## Moiety I comprises approximately 30 to 70mole percent of the wholly aromatic polyester, and preferablyapproximately 60 to 70 mole percent of the wholly aromatic polyester(e.g. approximately 60 mole percent). The melting point of the resultingwholly aromatic polyester tends to be lowered and the final fiberproperties optimized as one incorporates the p-oxybenzoyl moiety in themore preferred quantities.

The second key recurring unit (i.e., moiety II) of the wholly aromaticpolyester is m-oxybenzoyl moiety and possesses the structural formula:##STR4## Moiety II comprises approximately 3 to 10 mole percent of thewholly aromatic polyester, and preferably approximately 5 mole percentof the wholly aromatic polyester. The presence of the m-oxybenzoylmoiety in the wholly aromatic polyester (as described) has been found torender the polymer melt processable at even lower temperatures than ifthis component were omitted.

The third key recurring unit (i.e, moiety III) of the wholly aromaticpolyester is a 2,6-dicarboxynaphthalene moiety of the structuralformula: ##STR5## It is essential that moiety III consists of a pair offused benzene rings as illustrated rather than a single divalent benzenering. For instance, it has been found that if one were to substitutesingle benzene rings (i.e., a p-dioxyphenylene moiety) for a substantialportion of the naphthalene rings of moiety II, the properties of theresulting wholly aromatic polyester would be substantially different andadversely influenced as evidenced by substantially higher flow and melttemperatures resulting in significant degradation on processing.Commonly, moiety III comprises approximately 10 to 32.5 mole percent ofthe wholly aromatic polyester, and preferably approximately 10 to 18.5mole percent when forming a preferred wholly aromatic polyester (e.g.approximately 15 mole percent).

The fourth key recurring unit (i.e., moiety IV) of the wholly aromaticpolyester is a symmetrical dioxy aryl moiety of the formula --O--Ar--O--where Ar is a divalent radical comprising one or more fused or separatearomatic rings (i.e., at least one aromatic ring). Moiety IV issymmetrical in the sense that the divalent bonds which join the moietyto other moieties in the main polymer chain are symmetrically disposedon one or more aromatic rings (e.g., are para to each other ordiagonally disposed when present on a naphthalene ring). Commonly,moiety IV comprises approximately 10 to 32.5 mole percent of the whollyaromatic polyester, and preferably approximately 10 to 18.5 mole percentof the wholly aromatic polyester, and preferably approximately 10 to18.5 mole percent of the wholly aromatic polyester (e.g. approximately15 mole percent). Preferred moieties which may serve as the symmetricaldioxy aryl moiety in the wholly aromatic polyester of the presentinvention include: ##STR6## and mixtures of the foregoing.

The particularly preferred moiety IV is ##STR7##

Other ester-forming moieties (e.g. dicarboxy or dioxy units) other thanthose previously discussed additionally may be included in the whollyaromatic polyester of the present invention in a minor concentration solong as such moieties do not adversely influence the desiredthermotropic melt phase exhibited by the polyester heretofore definedand do not raise the melting point of the resulting polymer above thatspecified. As will be apparent to those skilled in the art, the totalmolar quantities of dicarboxy units and dioxy units present within thewholly aromatic polyester will be substantially equal. For instance, themolar quantities of moieties III and IV commonly are substantiallyequal. The various moieties upon polymer formation will tend to bepresent in a random configuration.

The wholly aromatic polyesters of the present invention commonly exhibit##STR8## end groups depending upon the synthesis route selected. As willbe apparent to those skilled in the art, the end groups optionally maybe capped, e.g., acidic end groups may be capped with a variety ofalcohols, and hydroxyl end groups may be capped with a variety oforganic acids. For instance, end capping units such as phenylester##STR9## and methylester ##STR10## optionally may be included at the endof the polymer chains. The polymer also may be oxidatively cross-linkedto at least some degree, if desired, by heating in an oxygen-containingatmosphere (e.g., in air) while in bulk form or as previously shapedarticle at a temperature below its melting point for a limited period oftime (e.g., for a few minutes).

The wholly aromatic polyesters of the present invention tend to besubstantially insoluble in all common polyester solvents, such ashexafluoroisopropanol and o-chlorophenol, and accordingly are notsusceptible to solution processing. They can surprisingly be readilyprocessed by common melt processing techniques as discussed hereafter.Some solubility is discernable in pentafluorophenol.

The wholly aromatic polyesters commonly exhibit a weight averagemolecular weight of about 2,000 to 200,000, and preferably about 10,000to 25,000 e.g., about 20,000 to 22,000. Such molecular weight may bedetermined by standard techniques not involving the solutioning of thepolymer, e.g., by end group determination via infra red spectroscopy oncompression molded films.

The wholly aromatic polyesters additionally commonly exhibit an inherentviscosity (i.e., I.V.) of approximately 0.5 to 7, preferably 2 to 3.3,and most preferably 2.5 to 3.1 when dissolved in a concentration of 0.1percent by weight in pentafluorophenol at 60° C.

The wholly aromatic polyesters of the present invention can beconsidered crystalline in the sense that fibers melt extruded therefromexhibit x-ray diffraction patterns using Ni-filtered CuKα radiation andflat plate cameras characteristic of polymeric crystalline materials. Inspite of the crystallinity observed, the wholly aromatic polyesters ofthe present invention nevertheless may be easily melt processed.

Unlike the aromatic polyesters commonly encountered in the prior art thewholly aromatic polyesters of the present invention are not intractableand form a thermotropic melt phase whereby an atypical degree of orderis manifest in the molten polymer. The subject polyester readily formsliquid crystals in the melt phase and accordingly exhibits a hightendency for the polymer chains to orient in the shear direction. Suchthermotropic properties are manifest at a temperature which is amenablefor melt processing to form shaped articles. Such anisotropy in the meltmay be confirmed by conventional polarized light techniques wherebycross-polaroids are utilized. More specifically, the thermotropic meltphase may conveniently be confirmed by the use of a Leitz polarizingmicroscope at a magnification of 40X with the sample on a Leitz hotstage and under a nitrogen atmosphere. The polymer melt is opticallyanisotropic, i.e., it transmits light when examined between crossedpolaroids. The amount of light transmitted increases when the sample issheared (i.e., is made to flow), however, the sample is opticallyanisotropic even in the static state. On the contrary, typical aromaticpolyesters do not transmit light to any substantial degree when examinedunder identical conditions.

The wholly aromatic polyester of the present invention may be formed bya variety of ester-forming techniques whereby organic monomer compoundspossessing functional groups which upon condensation form the requisiterecurring moieties are reacted. For instance, the functional groups ofthe organic monomer compounds may be carboxylic acid groups, hydroxylgroups, ester groups, acid halides, etc. For instance, the organicmonomer compounds may be reacted in the absence of a heat exchangefluid. They accordingly may be heated initially via a solid phasecondensation procedure with the temperature being progressively raiseduntil it exceeds the polymer's melting point and with the reactioncontinuing via a melt condensation procedure. A vacuum may be applied tofacilitate removal of volatiles formed during the condensation (e.g.,acetic acid or water). Also a slurry system may be utilized initiallywith the reaction being completed in the melt.

As set forth in commonly assigned U.S. Ser. No. 686,189, filed May 13,1976, of Gordon W. Calundann, entitled "Improved Melt ProcessableThermotropic Wholly Aromatic Polyester and Process for Its Production"is described a slurry polymerization process which may be employed toform the wholly aromatic polyester of the present invention. Thedisclosure of this copending application is herein incorporated byreference.

More specifically, in such technique, the organic monomer reactants fromwhich the p-oxybenzoyl moiety (i.e., moiety I), m-oxybenzoyl moiety(i.e., moiety II), and the symmetrical dioxy aryl moiety (i.e., moietyIV) are derived are initially provided in a modified form whereby theusual hydroxyl groups of these monomers are esterified (i.e., they areprovided as acyl esters). For instance, lower acyl esters of p-hydroxybenzoic acid and m-hydroxy benzoic acid wherein the hydroxy group isesterified and lower acyl diesters of aryl diols may be provided asreactants. The lower acyl groups preferably have from 2 to about 4carbon atoms. Preferably the acetate esters of the organic compoundswhich form moieties II and IV are provided. Accordingly, particularlypreferred reactants for condensation with 2,6-naphthalene dicarboxylicacid are p-acetoxybenzoic acid, m-acetoxybenzoic acid, and hydroquinonediacetate. If minor quantities of other aryl reactants (as previouslydiscussed) optionally provide oxy-units within the resulting polymer,these too preferably are provided as the corresponding lower acylesters.

Relative quantities of organic monomer reactants are provided in thereaction zone so that the potential dicarboxy units and dioxy unitsavailable for incorporation in the resulting wholly aromatic polyesterare substantially equal.

In accordance with a slurry polymerization technique the reactants(e.g., p-acetoxybenzoic acid, m-acetoxybenzoic acid, 2,6-naphthalenedicarboxylic acid, and hydroquinone diacetate) are provided in an inertheat exchange medium which preferably serves as a solvent for at leastone of the reactants. Typically, the 2,6-naphthalene dicarboxylic acidreactant is substantially soluble in the inert heat exchange medium andis present therein as a finely divided solid. As the polymer forms, itis insoluble in the inert heat exchange medium and assumes theconfiguration of a fine dispersion. The heat exchange medium preferablypossesses a boiling point in excess of the maximum polymerizationtemperature utilized. Those inert heat exchange media having boilingranges of about 350° to 400° C. are particularly preferred.Representative heat exchange media include the terphenyls: a eutecticmixture of 73.5 percent diphenyl oxide and 26.5 percent diphenyl,commercially available from the Dow Chemical Co. under the trademarkDowtherm A; and mixtures of polychlorinated polyphenyls such aschlorinated biphenyls typified by those commercially available from theMonsanto Co. under the trademark Therminol FR; terphenyls and mixturesthereof such as those composed of meta and para isomers commerciallyavailable from the Monsanto Co. under the trademark Therminol (e.g.,Therminol 88, 77, or 66); diphenylsulfone; other arylsulfones, such assubstituted diphenyl sulfones (e.g., ditolysulfone), etc. The relativequantity (weight:weight) of inert heat exchange medium to reactants inthe reaction zone typically is in the ratio of heat exchange medium tototal reactants of about 0.2:1 to 4:1, and most preferably about 2:1.

The slurry polymerization reaction may be carried out on a batch,continuous, or semicontinuous basis. Typical polymerization reactionscommonly are carried out at a temperature of at least about 200° C. upto a temperature below the melting temperature or decompositiontemperature of the resulting wholly aromatic polyester, e.g., at about200 to 275° C. In a preferred embodiment of the slurry process thetemperature of the slurry is increased as the polymerization reactionprogresses. A gradual or stepwise temperature increase during thepolymerization has been found to insure the formation of a superiorproduct. The polymerization reaction is preferably carried out withagitation at atmospheric pressure under an inert gas blanket with thecondensation reaction by-products (e.g., acetic acid) being continuouslyremoved from the reaction zone. Superatmospheric or subatmosphericpressures optionally can be utilized usually without commensurateadvantage. Typical reaction times commonly range from about 2 to 30hours, or more, with the lesser reaction times being possible when thereaction is catalyzed.

Representative catalysts for use in the process include dialkyl tinoxide (e.g., dibutyl tin oxide), diaryl tin oxide, titanium dioxide,alkoxy titanium silicates, titanium alkoxides, alkali and alkaline earthmetal salts of carboxylic acids, the gaseous acid catalysts such asLewis acids, hydrogen halides (e.g., HCl), etc. The quantity of catalystutilized typically is about 0.001 to 1 percent by weight based upon thetotal monomer weight, and most commonly about 0.01 to 0.2 percent byweight.

At the conclusion of the polymerization reaction the solid particulatewholly aromatic polyester (as defined) is recovered by any convenienttechnique. For instance, the solid particulate polymer conveniently maybe separated from the inert heat exchange medium (preferably followingcooling), by decantation, centrifugation, or filtration. It is thenwashed, and is dried. During the washing, residual heat exchange mediumadhering to the product may be removed by acetone, alcohols, lowhydrocarbons, methylene chloride, chloroform, benzene, toluene, etc., orany other relatively volatile solvent in which the heat exchange mediumis soluble.

The wholly aromatic polyester of the present invention readily can bemelt processed to form a variety of shaped articles, e.g., molded threedimensional articles, fibers, or films. The polyester of the presentinvention is also suited for molding applications and may be molded viastandard injection molding techniques commonly utilized when formingmolded articles. Unlike the wholly aromatic polyesters commonlyencountered in the prior art it is not essential that more severeinjection molding conditions (e.g., higher temperatures), compressionmolding, impact molding, or plasma spraying techniques be utilized.Fibers or films may be melt extruded.

When forming fibers and films the extrusion orifice may be selected fromamong those commonly utilized during the melt extrusion of such shapedarticles. For instance, the shaped extrusion orifice may be in the formof a rectangular slit when forming a polymeric film. When forming afilamentary material the spinneret selected may contain one andpreferably a plurality of extrusion orifices. For instance a standardconical spinneret containing 1 to 200 holes (e.g., 6 to 200 holes) suchas commonly used in the melt spinning of polyethylene terephthalate,having a diameter of about 5 to 60 mils (e.g., 10 to 40 mils) may beutilized. Yarns of about 20 to 36 continuous filaments are commonlyformed. The melt-spinnable wholly aromatic polyester is supplied to theextrusion orifice at a temperature above its melting point, e.g., atemperature of about 290° to 320° C.

Subsequent to extrusion through the shaped orifice the resultingfilamentary material or film is passed in the direction of its lengththrough a solidification or quench zone wherein the molten filamentarymaterial or film is transformed to a solid filamentary material or film.The resulting fibers commonly have a denier per filament of about 2 to50, and preferably a denier per filament of about 2 to 20.

The resulting filamentary or film optionally may be subjected to athermal treatment whereby its physical properties are further enhanced.The tenacity of the fiber or film particularly is increased by suchthermal treatment. More specifically, the fibers or films may bethermally treated in an inert atmosphere (e.g., nitrogen, argon, heliumor steam) or in a flowing oxygen-containing atmosphere (e.g., air) withor without stress at a temperature below the polymer melting point untilthe desired property enhancement is achieved. Thermal treatment timescommonly range from a few minutes to several days. As the fiber isthermally treated, its melting temperature progressively is raised. Thetemperature of the atmosphere may be staged or continuously increasedduring the thermal treatment or held at a constant level. For instance,the fiber may be heated at 250° C. for one hour, at 260° C. for onehour, and at 270° C. for 1 hour. Alternatively, the fiber may be heatedat about 15° to 20° C. below the temperature at which it melts for about48 hours. Optimum heat treatment conditions will vary with the specificcomposition of the wholly aromatic polyester.

The as-spun fibers formed from the wholly aromatic polyester of thepresent invention are fully oriented and exhibit highly satisfactoryphysical properties which render them suitable for use in highperformance applications. The as-spun fibers commonly exhibit an averagesingle filament tenacity of at least 5 grams per denier (e.g., about 5to 11 grams per denier), and average single filament tensile modulus ofat least about 300 grams per denier (e.g., about 400 to 700 grams perdenier), and exhibit an extraordinary retention of physical propertiesand dimensional stability at elevated temperature (e.g., at temperaturesof about 150° to 200° C.). Following thermal treatment (i.e., annealing)the fibers commonly exhibit an average single filament tenacity of atleast 10 grams per denier (e.g., 10 to 30 grams per denier), and anaverage single filament tensile modulus of at least 300 grams per deniermeasured at ambient conditions (e.g., 72° F. and 65 percent relativehumidity). Such properties enable the fibers to be used as tire cordsand in other industrial applications, such as conveyor belts, hose,cabling, resin reinforcement, etc. Films formed of the wholly aromaticpolyester of the present invention may be used as strapping tape, cablewrap, magnetic tape, electric motor dielectric film, etc. The fibers andfilms exhibit an inherent resistance to burning.

The following example is presented as a specific illustration of theclaimed invention. It should be understood, however, that the inventionis not limited to the specific details set forth in the example.

EXAMPLE

To a three-neck, round bottom flask equipped with a stirrer, nitrogeninlet tube, and a heating tape wrapped distillation head connected to acondenser are added the following:

(a) 58.54 grams p-acetoxybenzoic acid (0.325 mole)

(b) 4.50 grams m-acetoxybenzoic acid (0.025 mole)

(c) 16.21 grams 2,6-naphthalene dicarboxylic acid (0.075 mole)

(d) 14.56 grams hydroquinone diacetate (0.075 mole)

This mixture is brought to a temperature of 250° C. At 250° C. the2,6-naphthalene dicarboxylic acid is suspended as a finely divided solidin molten p-acetoxybenzoic acid, m-acetoxybenzoic acid and hydroquinonediacetate. The contents of the flask are stirred rapidly at 250° C.under a slow stream of dry nitrogen for about 2 hours while acetic acidis distilled from the polymerization vessel. The polymerizationsuspension is then raised to a temperature of 280° C. and is stirred atthis temperature for 3 hours under a nitrogen flow while additionalacetic acid is evolved. About 80 ml. of acetic acid is collected duringthese stages. The polymerization temperature is next increased to 320°C. The viscous polymer melt is held for 15 minutes at 320° C. under anitrogen flow and then subjected to a series of reduced pressure stages.The nitrogen is shut off and the pressure is reduced to about 300 mm. ofmercury for about 20 minutes, 210 mm. for 15 minutes, 70 mm. for 15minutes and finally about 0.2 mm. for 10 minutes. During these periodsthe polymer melt continues to increase in viscosity and is stirred moreslowly while the remaining acetic acid is removed from the reactionvessel. The polymer melt is next allowed to cool to ambient temperature(i.e., about 25° C.). Upon cooling, the polymer plug is finely ground ina Wiley Mill and dried in a forced air oven at 100° C. for 50 to 60minutes.

Approximately 54 grams of polymer are obtained. The inherent viscosity(I.V.) of the polymer is approximately 2.4 as determined inpentafluorophenol solution of 0.1 percent by weight concentration at 60°C. ##EQU1## where c = concentration of solution (0.1 percent by weight),and

ηrel = relative viscosity.

When the product is subjected to differential scanning calorimetry, itexhibits a large sharp endotherm at about 308° C. (peak), which repeatsat about 308° C. on subsequent remelt scans. The polymer melt isthermotropic.

When the melt is cooled in a differential scanning calorimeter at a rateof -20° C./min., a sharp polymer crystallization exotherm is observed atabout 264° C. (peak) indicating a rapid crystallization.

The resulting wholly aromatic polyester next is melt extruded to formoriented fibers directly from the melt or injection molded for formthree-dimensional shaped articles.

Although the invention has been described with preferred embodiments itis to be understood that variations and modifications may be employedwithout departing from the concept of the invention as defined in thefollowing claims.

I claim:
 1. A melt processable wholly aromatic polyester capable offorming a thermotropic melt phase at a temperature below approximately310° C., consisting essentially of the recurring moieties I, II, III,and IV wherein: ##STR11## and IV is a symmetrical dioxy aryl moiety ofthe formula --O--Ar--O-- where Ar is a divalent radical comprising atleast one aromatic ring, wherein said polyester comprises approximately30 to 70 mole percent of moiety I and approximately 3 to 10 mole percentof moiety II.
 2. A melt processable wholly aromatic polyester accordingto claim 1 which is capable of forming a thermotropic melt phase belowapproximately 300° C.
 3. A melt processable wholly aromatic polyesteraccording to claim 1 wherein said symmetrical dioxy arly moiety IV isselected from the group consisting of: ##STR12## and mixtures of theforegoing.
 4. A melt processible wholly aromatic polyester according toclaim 1 wherein said symmetrical dioxy aryl moiety IV is: ##STR13##
 5. Amelt processable wholly aromatic polyester according to claim 1 whereinthe molar quantities of III and IV are substantially equal.
 6. A meltprocessable wholly aromatic polyester according to claim 1 whichcomprises approximately 30 to 70 mole percent of moiety I, approximately3 to 10 mole percent of moiety II, approximately 10 to 32.5 mole percentof moiety III, and approximately 10 to 32.5 mole percent of moiety IV.7. A melt processable wholly aromatic polyester according to claim 1which comprises approximately 60 to 70 mole percent of moiety I,approximately 3 to 10 mole percent of moiety II, approximately 10 to18.5 mole percent of moiety III, and approximately 10 to 18.5 molepercent of moiety IV.
 8. A molded article comprising the meltprocessable wholly aromatic polyester of claim
 1. 9. A molding compoundcomprising the melt processable wholly aromatic polyester of claim 1which incorporates approximately 1 to 60 percent by weight of a solidfiller and/or reinforcing agent.
 10. A fiber which has been melt spunfrom the wholly aromatic polyester of claim
 1. 11. An improved meltprocessable wholly aromatic polyester capable of forming a thermotropicmelt phase at a temperature below approximately 310° C. consisting ofthe recurring moieties I, II, III, and IV wherein: ##STR14## wherein thepolyester comprises approximately 30 to 70 mole percent of moiety I,approximately 3 to 10 mole percent of moiety II, approximately 10 to32.5 mole percent of moiety III, and approximately 10 to 32.5 molepercent of moiety IV.
 12. A melt processable wholly aromatic polyesteraccording to claim 11 which is capable of forming a thermotropic meltphase below approximately 300° C.
 13. A melt processable wholly aromaticpolyester according to claim 11 wherein the molar quantities of moietiesIII and IV are substantially equal.
 14. A melt processable whollyaromatic polyester according to claim 11 which comprises approximately60 to 70 mole percent of moiety I, approximately 3 to 10 mole percent ofmoiety II, approximately 10 to 18.5 mole percent of moiety III, andapproximately 10 to 18.5 mole percent of moiety IV.
 15. A meltprocessable wholly aromatic polyester according to claim 11 whichcomprises approximately 65 mole percent of moiety I, approximately 5mole percent of moiety II, approximately 15 mole percent of moiety III,and approximately 15 mole percent of moiety IV.
 16. A molded articlecomprising the melt processable wholly aromatic polyester of claim 11.17. A molding compound comprising the melt processable wholly aromaticpolyester of claim 11 which incorporates approximately 1 to 60 percentby weight of a solid filler and/or reinforcing agent.
 18. A fiber whichhas been melt spun from the wholly aromatic polyester of claim 11.